A) Field Of The Invention
This invention relates to a quantum dot having core-shell structure.
B) Related Art
One of the uses of quantum dot including a semiconductor material is fluorescence generator. This type of quantum dot can generate fluorescent light of a predetermined wavelength in response to irradiation of light or particle of high energy. Such a quantum dot having core-shell structure in which a core made of such material as CdSe, CdS, InP, or GaP is covered with a shell layer or shell layers made of such material as ZnS, ZnSe, or the like has been proposed (for example, Japanese Unexamined Patent Application Publication No. 2011-76827). Core-shell structure in which a core of a III-V semiconductor (InGaN) is covered with a shell or shells of II-VI semiconductor (ZnO, ZnS, ZnSe, ZnTe, or the like) has also been proposed (for example, Japanese Unexamined Patent Application Publication No. 2010-155872).
Now, such quantum dots as CdSe/ZnS, InP/ZnS, or the like, in which a shell having a large energy gap is laminated on a core having a small energy gap, are used as visible light range quantum dots. When core-shell structure is made of different compound materials, there occurs generally lattice mismatch (CdSe/ZnS: 11.1%, InP/ZnS: 7.8%). The lattice mismatch will cause crystal lattice strain and may become causes of degradation in light emission efficiency and reliability.
There is proposal in which degradation in light emission efficiency by lattice mismatch is discussed as a problem, and fluorescence nanoparticle (multilayered core-shell structure of III-V semiconductor mixed crystals) in which a core of III-V In1-xnGaxA mixed crystal (A=N or P) is covered with a plurality of shell layers made of III-V In1-xnGaxnA mixed crystal, where composition is selected as x<xn<xn+1 (for example, Japanese Unexamined Patent Application Publication No. 2012-87220).